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One of the important contributions evergreens can make to landscaping is the abatement of noise. While exact correlations between planting evergreens and reducing decibels of environmental noise remain in question, there is general agreement that evergreens, often in conjunction with other noise-abatement measures, soften, diffuse and diminish irritating noises from traffic, industrial activity or even the neighbors. Use evergreen trees and shrubs to create a quieter and more restful outdoor environment in your yard.

Plantings and Measurable Noise Reduction

Studies by the United States Federal Highway Administration suggest that, while solid barriers such as walls, earth berms and buildings insulate neighboring residential areas from noise more effectively than plants, natural plantings have two major affects on the perception of noise. One is measurable noise reduction, estimated at between 3 and 5 decibels per 100 feet of thickness of a planted barrier. Other studies document greater noise reduction from placing a planted barrier close to the source of the noise rather than close to the source of perception. According to arborist Andrew Johnson, noise generated by traffic under 40 miles an hour can be reduced by planting a 20- to 50-foot-wide buffer within 20 to 50 feet of the traffic lane closest to the property being buffered. A similar barrier must be 65 to 100 feet wide to abate noise from traffic traveling faster than 40 mph. Combining evergreen planting with raised earth berms increases abatement potential.

Other Affects

The most powerful impact of evergreen planting for noise-abatement appears to be psychological, according to the U.S. FHWA. Visual screening of noise sources reduces their perceived impact. Getting noise sources out of sight as well as out of hearing is a strategy employed by residential, industrial and transportation planners at all levels. The State of California has gone so far as to make a Noise Element feature a legal requirement for all general development urban and rural plans. Together with a required Landscape Element, planning must address using plantings that are fire resistant, pest resistant and high in habitat value as well as useful for noise and noise-perception screening.

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Evergreens and Sound Buffering

Several characteristics distinguish plants that function effectively in a sound-buffering plan. Since a noise-impacted residence may be located above the noise source, plant height is important to creating an effective barrier. Other valuable qualities include thick fleshy leaves, abundant branches and branches that reach to the ground, so that a planted screen does not lose its effectiveness when plants grow. Above all, year-round durability makes a major contribution to noise buffering.

Choosing Evergreens

Numerous evergreens fulfill the criteria, but long life and easy maintenance are best assured by choosing trees and tall shrubs native to your area and climate zone. Natives possess strong resistance to pests and need less water and fertilizer than non-native plants. In areas where fire resistance is an issue, native plants may be required for certain areas. Your community's general plan may require or restrict the varieties of evergreens you can use for noise and other screening.

California Native Evergreens

California native evergreens include cypresses and pines. Native pines, among them ponderosa, knobcone, bishop, Monterey and gray pine, grow to mature heights of between 40 and 50 feet. Cypresses, including tecate and piute, grow to between 15 and 30 feet and are often well suited to dry locations. Plants that can be treated like multistemmed trees or large woody shrubs include Pacific wax myrtles, which can grow to 15 feet in height and a similar width and are valued as soil nitrogen-fixers. Manzanitas form a large family of tough bushy native evergreen shrubs ranging in size from 3 to 10 feet. Combining native evergreen trees with an under layer of evergreen shrubs can increase the density of your buffer at the trunk area of potentially tall trees.

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About the Author

Janet Beal has written for various websites, covering a variety of topics, including gardening, home, child development and cultural issues. Her work has appeared on early childhood education and consumer education websites. She has a Bachelor of Arts in English from Harvard University and a Master of Science in early childhood education from the College of New Rochelle.